Making a radius-sanding block

Long radius-sanding blocks for finish-sanding fingerboard
surfaces are a great help. Necks with cylindrical fretboard are
moved over these blocks, which are fastened on the workbench in a
lying position. As I am unfortunately not aware of any source of
such (long) radius-sanding blocks, you will have to make them
yourself. The one I am going to describe gets its
radius from three pieces of bent 3mm (1/8")- thick plywood.
With plywood thicker than that you won't get an even curve. The
base block can be built from five boards. The necessary height
(h) of the two side boards can be calculated for
any radius with the formula below. Spread glue between the plywood
sheets and screw them down along the center line.